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| United States Patent |
6,008,154
|
|
Rosendorfer
, et al.
|
December 28, 1999
|
Preparation of supported chromium catalysts
Abstract
Supported chromium catalysts are prepared by loading the support material
with chromium compounds and calcining at from 400 to 1100.degree. C., and
then treating the catalyst with a water-containing inert gas mixture.
| Inventors:
|
Rosendorfer; Philipp (Neustadt, DE);
Eck; Peter (Bad Durkheim, DE)
|
| Assignee:
|
BASF Aktiengesellschaft (Ludwigshafen, DE)
|
| Appl. No.:
|
948068 |
| Filed:
|
October 9, 1997 |
Foreign Application Priority Data
| Oct 22, 1996[DE] | 196 43 512 |
| Current U.S. Class: |
502/319; 502/150; 502/151; 502/152; 502/171 |
| Intern'l Class: |
B01J 023/26 |
| Field of Search: |
502/150,151,152,171,305,319
|
References Cited
U.S. Patent Documents
| 3671432 | Jun., 1972 | Peters et al. | 502/246.
|
| 4233139 | Nov., 1980 | Murrell et al. | 208/112.
|
| 4801572 | Jan., 1989 | Hsieh et al. | 502/242.
|
| 5006506 | Apr., 1991 | Hsieh et al. | 502/204.
|
| 5093300 | Mar., 1992 | Vogels et al. | 502/256.
|
| 5364915 | Nov., 1994 | Benham et al.
| |
| 5543376 | Aug., 1996 | Bergmeister | 502/117.
|
| Foreign Patent Documents |
| 186 174 | Jul., 1986 | EP.
| |
| 640 625 | Mar., 1995 | EP.
| |
| 1604708 | Dec., 1981 | GB.
| |
| 97/19963 | Jun., 1997 | WO.
| |
Other References
M.P. McDaniel, Advances in Catalysis, vol. 33, pp. 47-98, 1985, no month
available.
|
Primary Examiner: Wood; Elizabeth D
Attorney, Agent or Firm: Keil & Weinkauf
Claims
We claim:
1. A supported chromium catalyst for the polymerization of .alpha.-olefins
prepared by the process comprising loading the support material with
chromium compounds and calcining at from 400 to 1100.degree. C., wherein
the catalyst is treated with a water-containing inert gas mixture after
calcination at a temperature of from 20 to 100.degree. C. such that the
chromium catalyst has an adsorbed water content of from 0.05 to 1.0% by
weight, based on the total mass of the catalyst.
2. A supported chromium catalyst as claimed in claim 1, wherein the support
material used is SiO.sub.2, Al.sub.2 O.sub.3, MgO, ZrO.sub.2, TiO.sub.2,
B.sub.2 O.sub.3, CaO, ZnO or mixtures of these.
3. A supported chromium catalyst as claimed in claim 1, wherein the support
material used is silica gel.
4. A supported chromium catalyst as claimed in claim 1, wherein the
calcination is carried out at from 500 to 800.degree. C.
5. A supported chromium catalysts as claimed in claim 1, wherein the
treatment with the water-containing inert gas mixture is carried out in a
gas-phase fluidized bed.
6. A supported chromium catalyst as claimed in claim 1, wherein the
treatment with the water-containing inert gas mixture is carried out at
from 30 to 80.degree. C.
7. The catalyst of claim 1 wherein the inert gas is nitrogen.
Description
The present invention relates to a process for preparing supported chromium
catalysts by loading the support material with chromium compounds and
calcining at from 400.degree. C. to 1100.degree. C.
The present invention further relates to supported chromium catalysts
obtainable by this process, and also the use of these chromium catalysts
for the polymerization of .alpha.-olefins.
PRIOR ART AND BACKGROUND
Supported chromium compounds have long been known as catalysts for the
polymerization of .alpha.-olefins (see, for example, M. P. Mc Daniel, Adv.
Cat 33, (1985) 47-98). The preparation of such supported chromium
catalysts is usually carried out in two stages. In a first step, the
support material is first brought into contact with a soluble chromium
compound in a suitable solvent. Subsequently, in a second step, the
mixture of support and chromium compound is calcined in a stream of air or
oxygen at high temperatures, for instance from 400 to 1100.degree. C.
(see, for example, U.S. Pat. No. 5,363,915).
It is known that the chromium catalysts can very easily be inactivated by
catalyst poisons during the polymerization reaction. In EP-A-0 640 625,
for example, states that it is extremely important to thoroughly remove
such catalyst poisons such as moisture, oxygen, carbon monoxide, carbon
dioxide and acetylene from the polymerization gas and that, for example, 2
ppm of carbon monoxide are sufficient to dramatically impair the
polymerization.
The catalyst and polymer properties are influenced significantly by the
composition of the support, the support structure (pores volume, mean pore
radius, etc.), the calcination temperature and the chromium content. High
polymer molecular weights can be achieved, for example, by a lower
calcination temperature, although an often undesired broadening of the
molecular weight distribution results.
THE INSTANT INVENTION
It is an object of the present invention to find a process for preparing
supported chromium catalysts which leads to catalysts which make possible
the preparation of polymers having high molecular weights and narrow
molecular weight distributions.
We have found that this object is achieved by a process for preparing
supported chromium catalysts by loading the support material with chromium
compounds and calcining at from 400 to 1100.degree. C., wherein the
catalyst is treated with a water-containing inert gas mixture after
calcination.
Furthermore, we have found a supported chromium catalyst which is
obtainable by the process of the present invention, and also the use of
this supported chromium catalyst for the polymerization of
.alpha.-olefins.
The loading of support materials with soluble chromium compounds is
generally known. Particularly suitable support materials are inorganic
compounds, in particular porous oxides such as SiO.sub.2, Al.sub.2
O.sub.3, MgO, ZrO.sub.2, TiO.sub.2, B.sub.2 O.sub.3, CaO, ZnO or mixtures
of these. The support materials preferably have a particle diameter of
from 1 to 300 .mu.m, in particular from 30 to 70 .mu.m. Particularly
preferred supports are, for example, silica gels and aluminosilicate gels,
preferably those of the formula SiO.sub.2 . a Al.sub.2 O.sub.3, where a is
a number in the range from 0 to 2, preferably from 0 to 0.5; these are
thus aluminosilicates or silicon dioxide. Such products are commercially
available, eg. Silica Gel 332 from Grace.
The doping of the catalyst support with the chromium-containing active
components is preferably carried out from a solution or, in the case of
volatile compounds, from the gas phase. Suitable chromium compounds are
chromium(VI) oxide, chromium salts such as chromium(III) nitrate,
chromium(III) acetate, complexes such as chromium(III) acetylacetonate or
chromium hexacarbonyl, or else organometallic compounds of chromium such
as bis(cyclopentadienyl)chromium(II), organic chromic(VI) acid esters or
bis(arene)chromium(O).
The loading of the support is generally carried out by bringing the support
material in a solvent into contact with a chromium compound, removing the
solvent and calcining the catalyst at from 400 to 1100.degree. C. For this
purpose, the support material can be suspended in a solvent or in a
solution of the chromium compound.
The support system can be loaded not only with the chromium-containing
active component but also with further dopants. Possible dopants are, for
example, compounds of boron, fluorine, aluminum, silicon, phosphorus or
titanium. These dopants are preferably applied to the support together
with the chromium compounds, but can also be applied to the support in a
separate step before or after loading with chromium.
Suitable solvents for the doping of the support are, for example, water,
alcohols, ketones, ethers, esters and hydrocarbons.
The concentration of the doping solution is generally 0.1-200 g of chromium
compound/1 of solvent, preferably 1-50 g/l.
The weight ratio of the chromium compounds to the support during loading is
generally from 0.001:1 to 200:1, preferably from 0.005:1 to 100:1.
After the doping of the support, the dry catalyst precursor is calcined at
from 400 to 1100.degree. C., for example in an oxidizing,
oxygen-containing atmosphere in a fluidized bed reactor. The calcined
product is preferably cooled under an inert gas atmosphere to prevent
adsorption of oxygen. This calcination can also be carried out in the
presence of fluorine compounds such as ammonium hexafluorosilicate, by
means of which the catalyst surface is modified with fluorine atoms.
In a preferred embodiment of the process of the present invention, the
calcination is carried out at from 500 to 800.degree. C.
After cooling, the supported catalyst is treated with a water-containing
inert gas mixture. Nitrogen is particularly suitable as inert gas, but it
is also possible to use, for example, noble gases such as argon or
mixtures of such inert gases.
The treatment with the water-containing inert gas mixture is generally
carried out at from 20 to 100.degree. C., preferably from 30 to
800.degree. C.
Like the calcination, the treatment with the water-containing inert gas
mixture can also be carried out, for example, in a predominantly immobile
bed. However, the latter treatment is preferably also carried out in a
fluidized bed.
The selected water content of the inert gas depends on both the time and
temperature of the treatment. In the case of a low water content, the
treatment takes a longer period of time. These parameters are generally
chosen such that the water content of the, supported catalyst subsequently
reaches the desired value. This can be easily determined in a few
preliminary experiments. The inert gas is advantageously loaded with water
by passing an inert gas stream through the desired volume of water until
this amount of water has been completely carried away by the gas.
Preference is given to chromium catalysts of the present invention which
have an adsorbed water content of from 0.05 to 1.0% by weight, based on
the total mass of the catalyst. Particular preference is given to an
adsorbed water content of from 0.1 to 0.7% by weight, in particular from
0.2 to 0.4% by weight. The water content can here be determined by
differential thermogravimetry.
In polymerization reactions of .alpha.-olefins, the catalysts of the
present invention lead to productivities which are comparable to those
given by corresponding untreated catalysts, but the polymers have a higher
molecular weight and also a narrower molecular weight distribution. In
addition, the water treatment significantly improves the flow behavior of
the supported catalyst and thus significantly improves the meterability.
The catalysts of the present invention can be advantageously used for the
polymerization of .alpha.-olefins.
In these polymerization processes, the pressure is generally from 100 to
10000 kPa, preferably from 1000 to 6000 kPa, and the temperature is
generally in the range from 10 to 150.degree. C., preferably from 30 to
125.degree. C.
The supported chromium catalysts are very well suited to the polymerization
and oligomerization of .alpha.-olefins, preferably C.sub.2 -C.sub.10
-alk-1-enes such as ethylene, propene, 1-butene, 1-pentene, 1-hexene,
1-heptene, 1-octene, 1-nonene or 1-decene.
In particular, ethylene can be homopolymerized or copolymerized with
C.sub.3 -C.sub.10 -alk-1-enes, for example with propene, 1-butene,
1-hexene, 1-octene or 1-decene or mixtures of these, with the mixing ratio
not being critical for the effectiveness of the catalyst.
The polymerization of the alk-1-enes can be carried out by the customary
processes for the polymerization of olefins, for example solution
processes, suspension processes, stirred gas-phase or gas-phase fluidized
bed processes, continuously or batchwise.
The catalysts are particularly well suited for polymerizations by the
suspension process and the gas-phase fluidized bed process.
To provide further control of the molecular weights, it can be advantageous
to use hydrogen as regulator in the polymerization. Details of this
regulation method are known to those skilled in the art.
Furthermore, it has been found to be advantageous to carry out the
polymerization in the presence of organometallic compounds. Suitable
organometallic compounds are, for example, alkyls of main groups I and II
of the Periodic Table of the Elements, and also of aluminum. Particularly
preferred metal compounds are n-butyllithium, n-butyl-n-octylmagnesium,
n-butyl-n-heptylmagnesium, tri-n-hexylaluminum, triisobutylaluminum,
triethylaluminum and timethylaluminum. These organometallic compounds are
usually used in such amounts that the molar ratio of their metal atoms to
chromium is from 1:0.01 to 1:100, preferably from 1:0.1 to 1:10.
EXAMPLES
Example 1
Preparation of a Supported Catalyst
100 g of silica gel (type SG 332, from Grace, Worms, pore volume: 1.7 ml/g,
specific surface area by the BET method: 220 m.sup.2 /g) were suspended in
250 ml of methanol under a nitrogen atmosphere. A solution of 2.3 g of
Cr(NO.sub.3).sub.3 .times.9H.sub.2 O in 80 ml of methanol were added to
the suspension. The suspension was stirred for 10 minutes and then freed
of solvent by distillation under reduced pressure. The residue was
subsequently calcined at 600.degree. C. in an air-fluidized bed for 10
hours. The bed was cooled by passing dry nitrogen through it.
Subsequently, water-containing nitrogen was passed through the fluidized
bed at 50.degree. C. until the catalyst had absorbed 0.3% by weight of
water.
Preparation of a comparative catalyst not according to the present
invention
A comparative catalyst was prepared as described in Example 1, but without
final treatment with water-containing nitrogen.
Example 2
Polymerization of Ethylene
A stirable 10 1 pressure autoclave was heated to 95.degree. C. and flushed
a number of times with ethylene. While stirring, 500 ml of isobutane were
introduced into the reactor and ethylene was injected until a pressure of
40 bar was reached. 500 mg of catalyst and 90 mg of tri-n-hexylaluminum
were subsequently metered into the autoclave via a pressure lock. The
pressure was kept constant during the polymerization by addition of
ethylene. After 90 minutes, the polymerization was stopped by venting the
reactor. The results are shown in the following table.
______________________________________
Productivity
M.sub.w
M.sub.n
M.sub.w
Viscosity
HLMI
Catalyst [g/g] [10.sup.3 ] [10.sup.3 ] M.sub.n [dl/g] [g/10 min]
______________________________________
According
3500 715 36 20 6.7 0.2
to Exp 1
Comparative 3400 597 23 26 5.4 3.3
catalyst
______________________________________
The example shows that the catalyst according to the present invention
leads to a polymer having a higher molecular weight and a narrower
molecular weight distribution expressed by the quotient M.sub.w /M.sub.n.
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